1. Field of the Invention
The present invention relates to techniques for recovering liquids on the surface of a body of water and, more particularly, to improved skimming techniques for recovering hydrocarbon-based fluids, such as oil or gasoline, from the surface water.
2. Description of the Background
Various equipment has been devised for recovering low density fluids, such as oil, from surface water. In most cases, the recovery of this oil is required due to the adverse environmental consequences of oil in a water supply. Probably the most widely used equipment for this purpose is skimming equipment, which separates the oil from the water by allowing the oil to naturally float to the surface of the water due to the density variance. Conventional skimming equipment uses a weir to separate the oil (with some water) from the remaining body of water. Permanent skimming equipment is commonly in place, for example, in waste treatment ponds adjacent industrial and petrochemical facilities to recover small quantities of oil discharged with water from the facility before the water is returned to a river or other water supply.
When oil is unexpectedly encountered on the surface of a body of water, or is encountered in unusually high concentrations, it is often preferable to utilize a power driven hull to assist in hydrocarbon collection. Such hulls have, for example, been provided with endless belts which are lowered into the water to pick up the oil. The oil is removed from the belt by a squeegee device or other suitable extraction equipment. The collected oil is stowed in a compartment in the hull while the cleaned belt returns to the water. An advantage of this system is that the hull can be easily steered or manipulated to desired locations on the body of water which evidence large oil slicks.
Hulls also have been employed with hydrocarbon recovery systems utilizing a ring-shaped weir or boom to collect the oil within the perimeter of the boom and adjacent the hull so that the oil can be retrieved at a location adjacent the hull. The surface water containing the oil may be drawn into a holding tank in the hull. Alternatively, the oil may be allowed to rise to the surface of the water in the hull holding tank, so that the oil and some water can be collected in a separate tank while most of the water originally drawn into the hull is directed back to the pond or body of water.
Another type of skimming device is disclosed in U.S. Pat. No. 4,597,863. This hull-like device does not utilize a floating weir, but utilizes the engine propeller to draw the surface oil/water mixture into the hull, where the water is separated by a sophisticated oil/water separator within the vessel. This system has several significant advantages compared to a system which utilizes a external floating boom, particularly in that the hull may be easily manipulated to a location in the body of water where it may be most effective. The system is also designed so that the oil slick on the surface of the water will be drawn to the hull.
Although the hydrocarbon system described in the '863 patent has several significant advantages over other prior art hydrocarbon recovery techniques, it is relatively complex and thus expensive. In part, this complexity and expense is due to the sophisticated oil/water separator on the hull. Moreover, the unit is intended to prevent a frontal wake and minimize "pushing" the surface water away from the hull during the skimming operation, although its efficiency is limited by either decreased skimming speed, or the creation of a frontal wake and thus decreased oil recovery performance.
The disadvantages of the prior art are overcome by the present invention, and improved methods and apparatus are hereinafter disclosed for efficiently recovering low density fluids, such as hydrocarbons, on the surface of a body of water.